Newly released Arizona hospital data show severe dog bites increased dramatically in recent years, especially among children, confirming what until now has been largely anecdotal suspicion.

An Arizona Department of Health Services study released Thursday says that the number of inpatient hospitalizations — meaning the bite was severe enough to warrant at least one overnight stay — increased 139percent from 2008 to 2012.

Among all dog-bite injuries in the state during that period, the study found about a third were among children younger than 14. Dog-bite cases in Arizona hospitals cost $55million, about a third of which was paid by the taxpayer-funded state Medicaid system.

The exact cause of the increases is unclear, though there is one commonality: The majority of severe dog bites are occurring in the home.

Phoenix Children's Hospital also has been conducting a study on its rising number of severe dog bites. Hospital officials have found that the majority of dogs biting children are family dogs or otherwise known to those they bite, as opposed to strays.

"People have to remember, however much the dog is a family member and they love them and trust them, biology is biology," said Dr. Ramin Jamshidi, attending surgeon at Phoenix Children's Hospital and trauma center. "It's an animal. And if the child inadvertently provokes the pet, or the dog's confused, whatever the reason — the dog will revert to the inborn behavior."

Though the Health Department's study period ended in 2012, Phoenix Children's Hospital data show the increase continued through 2013.

The hospital also has seen a steady increase in the past six years in the number of children so badly bitten they required care by a trauma surgeon and, in some cases, a plastic surgeon.

State health Director Will Humble asked his staff last week to analyze the discharge data in light of the numerous severe cases reported in the past month. The department confirmed severe attacks have been on the rise, creating a growing public-health hazard.

"You hear more and more stories about bad maulings, and I was just curious if it really was an increasing trend or not," Humble said.

The most high-profile case in the past month was the Feb.20 mauling of 4-year-old Kevin Vicente by a pit bull in south Phoenix.

And on Wednesday, a Phoenix woman was attacked and severely injured by seven dogs.

The Maricopa County Animal Care and Control Unit has not seen a significant increase in reported dog bites since 2008.

But, experts say, the concentration of recent attacks should ring alarm bells for parents and dog owners; they should be as vigilant when their children are near pets as they would be with other known dangers.

"Just like you wouldn't leave your kids around water unsupervised, you shouldn't leave your kids around a dog unsupervised," said Dr. Jeffrey Salomone, trauma medical director at Maricopa Medical Center.

While it is unclear why more dog-bite victims are ending up in hospitals, some trends are evident. For example, more than 70 percent of dog bites reported during the period studied by the state Health Department occurred in homes.

Phoenix Children's Hospital officials found a large percentage of their dog-bite cases since 2008 involved a child provoking a dog — not necessarily by teasing the dog, but often by simply giving the dog a hug. The attacks involved more than two dozen different breeds.

In one case, a 2-month-old infant's testes were bitten off by a family dog. And a few months ago, a pit-bull puppy attacked a boy, severing his trachea.

Such attacks not only cause devastating physical injuries that can scar forever, but also psychological trauma, said Denice Twitchell, a pediatric-trauma nurse practitioner at Phoenix Children's Hospital.

They underscore the importance of taking precautions, Humble said.

"If you want to be a dog owner, make sure you pick a breed and a dog that matches your lifestyle," Humble said. "If you don't have kids yet, make sure you think about that. If you're going to have kids ... make that a part of your decision-making."

Parents should find out about dogs that may be present before sending their children to playdates or sleepovers, he said.

Kevin Vicente, 4, recovers at Maricopa Medical Center on March 20, 2014, after having surgery to help repair damage to his face caused by a dog bite. Pat Shannahan/The Republic

Kevin Vicente, 4, sits with Martha Martinez at Maricopa Medical Center on March 20, 2014, after Kevin underwent surgery to help repair damage caused to his face from a dog bite. Pat Shannahan/The Republic

Kevin Vicente, 4, sits with Martha Martinez at Maricopa Medical Center on March 20, 2014, after Kevin underwent surgery to help repair damage caused to his face from a dog bite. Pat Shannahan/The Republic

Kevin Vicente, 4, sits with Martha Martinez at Maricopa Medical Center on March 20, 2014, after Kevin underwent surgery to help repair damage caused to his face from a dog bite. Pat Shannahan/The Republic